The invention relates to a device for the electric measurement of a liquid level.
The invention relates particularly to a device for the electric measurement of the level of a liquid contained in a container, having a conductive foil, such as a temperature-dependent externally electrically heated resistance foil, immersed in the liquid and surrounded by a protective tube, the total resistance of which foil, detectable by an evaluation circuit, is dependent on the level of liquid in the container, or having a capacitance foil bearing two conductors which form a capacitor, the conductive foil being developed in strip-shape and being held in a helical shape by holding elements acting on its longitudinal edges within the protective tube in such a manner that the surface is washed over on both sides by the liquid, and the longitudinal edges of the conductive foil being spaced apart by a correspondingly large pitch from turn to turn.
German Patent No. 32 355 34 discloses such a device.
In this patent the prime objective was to create a device which makes it possible to measure a level with high precision. The helical development of the conductive foil stipulated in the above patent permits of a substantially greater length of the conductive foil than corresponds to its linear depth of immersion. In this way the wettable surface of the conductive foil becomes large so that the power of resolution of the measurement region becomes correspondingly large. Aside from this, the helical arrangement of the conductive foil makes it possible to bend the device as a whole in radial direction to a limited extent without the conductive foil being damaged.
Containers in which a liquid level must be measured are frequently of rather irregular shape. Automobile gasoline tanks frequently have very complicated shapes in order to make optimal use of the space available and to permit the largest possible tank volume. Such container developments frequently make it impossible for the device for the electric measurement of the liquid level to extend in a straight line down to the lowest point in the container. It is then necessary to bend the protective tube together with the conductive foil more strongly so that it can follow the construction of the container. In the device in accordance with the above patent, this possible flexibility was not sufficient in all cases.
It is an object of the invention further to develop a device of the aforementioned type in such a way that, while retaining the high precision of measurement, radial bending of the protective tube with the conductive foil installed in it is possible to the greatest possible extent.